Solid state photomultipliers (SSPMs), which are also commonly referred to as MicroPixel Photon Counters (MPPC) or MicroPixel Avalanche Photodiodes (MAPD) have become popular for use as photosensors. For example, SSPMs have been employed in scintillator based nuclear detectors. Typically, SSPMs are implemented as Silicon Photomultipliers (SiPM). The Silicon Photomultiplier (SiPM) is a multipixel array of avalanche photodiodes with a number up to a few thousand independent micropixels (with typical size of 10-100 microns) joined together on common substrate and working on common load. Each pixel detects the photoelectrons with a gain of about 106.
Conventionally, the output of an SSPM pixel is connected to a front end buffer amplifier, which can be implemented as a transimpedance amplifier. Using this conventional arrangement can result in a readout pulse from the SSPM having a readout pulse shape that exhibits a fast rise time (e.g., <1 ns) and a relatively slow fall time (e.g., 10-50 ns). However, the inventors have observed that as the size of the SSPM increases, the readout pulse shape response degrades significantly due to increased parasitic capacitance and inductance in combination with intrinsic impedance of each SSPM pixel.
Thus, the inventors have provided an improved solid state photomultiplier.